Electroplating smooth ductile gold



P 17, 1963 E. c. RINKER ETAL 3,104,212

ELECTROPLATING SMOOTH DUCTILE GOLD Filed May 21, 1959 FIG.3

INVENTOR. Edwin C.Rinker a Robert Duvo United States Patent 3,104,212 ELECTRQPLATBNG SMQOTH DUCTILE GOLD Edwin C. Rinker, Morristown, and Robert Duva,

Paramus, N..l., assignors to Sci-Rex Corporation, Nutley, N J a corporation of New Jersey Filed May 21, 1959, Ser. No. 814,758 18 Claims. tCi. 204-46) This invention relates to improvements in the process of producing a ductile electrochemical pure gold plate and to the electrolyte for producing the same.

Pure gold plate is customarily obtained from an alkaline reacitng cyanide electrolyte or rrom a very strongly acidic electrolyte such as chloroauric acid. These baths tend to produce rough and/or granular deposits which must be burnished and/ or scratch brushed to produce a satisfiactory deposit of heavy thickness. These baths also have poor metal distribution and therefore result in deposits which are wasteful due to the unequal distribution and to the losses during burnishing or scratch brushing. Furthermore, the deposits obtained from such baths do not have satisfactory machinability and do not produce a satisfiactory fragment when sliced.

Among the objects of the invention is to provide a process and an electrolyte bath for producing a ductile, hard, corrosion resistant gold deposit of gold color which deposit is smooth as it is removed from the bath.

Among other objects of the invention is to provide a stable, pure gold electroplating bath which is easily maintained, has good throwing power and is capable of producing uniform deposition when the temperature, pH, current density, agitation or cathode to anode ratio varies somewhat.

These objects and others ancillary thereto are obtained by providing a relatively weak acid bath containing l) a weak, stable, organic acid, and (2) gold as a cyanide (potassium gold cyanide, for example), the acidity of the bath being adjusted to pH 36.

Examples of acids which miay be employed are formic, acetic, citric, tartaric, lactic, kojic, or similar acids and mixtures of these acids. The acid should be present in proportions of about to 150 grams per liter and may be partially neutralized with ammonium or alkali hydrox ide to give a pH of about 36. It is this weak organic acid and the procedure of maintaining the bath within a limited pH range that produces the desired eifect of a gold deposition.

The gold may be added as the double cyanide or gold and an alkali metal, potassium gold cyanide for example, and may be present in proportions of about 1 gram per liter to 30 grams per liter of gold.

This application is a continuation-impart of US. application Serial No. 677,818, filed August 13, 1957, now Patent No. 2,905,601. In that application there is disclosed the process of preparing bright, ductile, alloy gold electrodcposits in a bath containing a weak stable organic acid, gold as a cyanide and one or more base metal salts, the acidity of the bath being adjusted to pH 3-5. Mirror bright deposits are obtained only when the base metal salts are added. Without the base metal calm, however, a smooth ductile deposit is obtained from such blaths which deposits are industrially useful because of their smoothness, their unusaully high degree of ductility, even at 'high temperatures, their high electrical and thermal conductivity, their impermeability to atmospheric and other gases and their machinability.

The bath may be operated at a current density of l to 100 amperes per square foot. Moderate to rapid agitation improves the operation. The bath may be operated at normal room temperature (70 P.) which is advantageous in that no thermostatic regulation is necessary but higher or lower temperatures of from 50 to 180 F. may be 3,104,212 Patented Sept. 17, 1963 employed. Since the bath is at a pH which does not attack base metal forms to be plated, high temperatures can be employed and the ductility of the product may be improved by plating at 90-480", for example.

The deposits obtained have the yellow color or pure gold, and are 24 karat gold.

The invention both as to its organization and its method of operation, together with additional objects and advantages thereof, will best be understood from the following description of specific embodiments.

In the drawings:

FIG. 1 is a view of an electrical conductor element which is advantageously plated with ductile gold of the present invention.

FIG. 2 is a side view of a base metal cylinder which is plated with the ductile gold of the present invention so that it can be sliced or machined.

FIG. 3 is a view of a plastic cylinder containing base metal ring plated with ductile gold so that the whole cylinder can be machined.

The following examples illustrate how the ductile platis obtained.

Example 1 An electrolytic bath is made by dissolving the following components:

G./liter Citric acid plus sodium citrate '80 Gold (as potassium gold cyanide) 8 Water Remainder The amount of sodium citrate is adjusted by adding the citrate or alkali until the bath has a pH of 3 to 6. A clean and polished steel or other metal body is made the cathode in said bath, at a current density or 10 amperes per square foot, while the bath is maintained at a temperature of about 70 F.

The deposit obtained from this bath is ductile, corrosion-resistant with a uniform, smooth, yellow-gold coloration. The gold deposits assay 24 karat gold. Deposits of thicknesses of 250-500 microns are readily obtained from this bath, without affecting the smoothness of the resultant deposit.

Example 2 An electrolytic bath is made by dissolving the following components:

G./liter Acetic acid and sodium acetate 50 Gold (as cyanide) 4 Water Remainder An electrolytic bath is made by dissolving the follow-. ing components:

G./liter Tartaric acid and sodium tartrate Gold (as potassium gold cyanide) 8 Water Remainder The pH of the bath is adjusted to 3-6 by addition of more acid or alkali. The deposit obtained from this bath under conditions such as specified in Example 1 is ductile, corrosion-resistant, and uniformly yellow in color.

The fineness of the deposit is 24 karat.

In the above examples, lactic acid, kojic acid, formic acid or similar organic acids may be substituted for the acetic, citric or tartaric acid specified. Such baths are brought to the proper pH by the addition of an alkali or the acid in use.

A smooth ductile plate such as obtained by the processes of Examples l-3 above is especially useful in conductor elements which are to be bend or crimped as in the device of FIG. 1. The conductor comprisses a male portion 11 for insertion into a female conducting socket and a U-shaped portion 12 which is to be crimped about the end 15 of a conducting wire 16 for example. The conductors 10 plated with a layer 20 of the ductile gold of the present application can be crimped in portion 12 without cracking or rupturing the gold plating.

Small parts such as gold plated ring shaped elements may be made by plating a cylinder with a layer of gold by the process of the present invention and thereafter slicing the cylinder 25 to produce appropriate size rings 26. Since the gold plate is ductile it is not injured by the cutting operation.

When ring elements made, for example, by slicing a cylinder 26 as shown in FIG. 2 are united to a plastic insulating cylinder 30 it is usually desirable to grind or polish the combined element so as to present a smooth outer surface. The cylinder 30 and rings 26 can be ground and polished without cracking the gold plated layer of rings 26.

The features and principles underlying the invention described above in connection with specific exemplifications will suggest to those skilled in the art many other modifications thereof. It is accordingly desired that the appended claims shall not be limited to any specific feature or details thereof.

We claim:

1. A method of electrodepositing smooth ductile gold which comprises electrolyzing a solution consisting essentially of 10-150 g./liter of a weak, stable organic acid, partially neutralized with alkali to provide a pH of 3-6, and 1-30 g./liter of gold added as a gold cyanide.

2. A method of electrodepositing smooth, ductile gold which comprises electrolyzing a solution consisting essentially of 10-150 g./liter of citric acid, partially neutralized with alkali to provide a pH of 3-6, and l-30 g./liter of gold added as a gold cyanide.

3. A method of electrodepositing smooth ductile gold which comprises electrolyzing a solution consisting essentially of 10-150 g./liter of tartaric acid, partially neutralized with alkali to provide a pH of 3-6 and 1-30 g./liter of gold added as a gold cyanide.

4. A method of electrodepositing smooth ductile gold which comprises electrolyzing a solution consisting essentially of 10-150 g./liter of acetic acid, partially neutralized with alkali to provide a pH of 3-6 and 1-30 g./liter of gold added as a gold cyanide.

5. An electrolyte for depositing smooth, ductile gold coatings consisting essentially of 10-50 g./ liter of a weak, stable organic acid partially neutralized with alkali to provide a pH of 3-6, and 1-30 g./liter of gold added as a gold cyanide.

6. An electrolyte for depositing smooth, ductile gold l coatings consisting essentially of 10-50 g./liter of citric acid partially neutralized with alkali to provide a pH of 3-6, and 1-30 g./liter of gold added as a gold cyanide.

7. An electrolyte for depositing smooth ductile gold coatings consisting essentially of 10-50 g./liter of tartaric acid partially neutralized with alkali to provide a pH of 3-6, and 1-30 g./ liter of gold added as a gold cyanide.

S. An electrolyte for depositing smooth ductile gold coatings consisting essentially of 10-50 g./liter of acetic acid partially neutralized with alkali to provide a pH of 3-6, and l-3O g./liter of gold added as a gold cyanide.

9. A method of electrodepositing gold which comprises electrolyzing a solution in which the initial ingre-. dients consist essentially of citric acid and a complex cyanide salt of an alkali metal and gold, said solution having a pH value of about 3-6.

10. A method of electrodepositing gold which comprises electrolyzing a solution in which the initial ingredients consist essentially of a weak stable organic acid, and a complex cyanide of an alkali metal and gold, said solution having a pH value of about 3-6.

11. The process of claim 10 in which the electrodeposition is carried out at a temperature of 50-180 F.

12. The process of claim 1 in which the electrodeposition is carried out at a temperature of 50-180 F.

13. The process of claim 10 in which the current density is 1-100 amperes per square foot.

14. The process of claim 1 in which the current density is 1-100 amperes per square foot.

15. A method of electrodepositing smooth ductile gold which comprises electrolyzing a solution in which the initial ingredients. consist essentially of water with 10-150 g./liter of a weak stable organic acid, 1-30 g./ liter of gold added as an alkali gold cyanide and sutlicient alkali to provide a pH of 3-6.

16. A method of electrodepositing smooth, ductile gold which comprises electrolyzing a solution in which the initial ingredients consist essentially of water with 10-150 g./liter of citric acid, 1-30 g./liter of gold added as an alkali gold cyanide and sufiicient alkali to provide a pH of 3-6.

17. A method of electrodepositing smooth, ductile gold which comprises electrolyzing a solution in which the initial ingredients consist essentially of water with 10-150 g./liter of tartaric acid, 1-30 g./liter of gold added as an alkali gold cyanide and sufficient alkali to provide a pH of 3-6.

18. ;A method of electrodepositing smooth, ductile gold which comprises electrolyzing a solution in which the initial ingredients consist essentially of water with 10-150 g./liter of acetic acid, 1-30 g./1iter of gold added as an alkali gold cyanide and sufiicient alkali to provide a pH of 3-6.

References Cited in the tile of this patent UNITED STATES PATENTS 2,905,601 Rinker et al. Sept. 22, 1959 

1. A METHOD OF ELECTRODEPOSITING SMOOTH DUCTILE GOLE WHICH COMPRISES ELECTROLYZING A SOLUTION CONSISTING ESSENTIALLY OF 10-150 G./LITER OF A WEAK, STABLE ORGANIC ACID, PARTIALLY NEUTRALIZED WITH ALKALI TO PROVIDE A PH OF 6-2 AND 1-30 G./LITHER OF GOLD ADDED AS A GOLD CYANIDE. 